The structure of Fe-Si alloy in Earth's inner core

Shigehiko Tateno, Yasuhiro Kuwayama, Kei Hirose, Yasuo Ohishi

    Research output: Contribution to journalArticlepeer-review

    52 Citations (Scopus)

    Abstract

    Phase relations of iron-silicon alloy (Fe-6.5 wt.% Si and Fe-9 wt.% Si) were investigated up to 407 GPa and 5960 K in a laser-heated diamond-anvil cell, which likely covers the entire pressure and temperature conditions of the Earth's inner core. Synchrotron X-ray diffraction measurements show that Fe-9 wt.% Si with a hexagonal close-packed (hcp) structure is stable to 4800 K at 330 GPa, corresponding to the pressure at the inner/outer core boundary, and decomposes into a mixture of Si-poor hcp and Si-rich CsCl-type (B2) phases at higher temperatures. We also found that the solubility of silicon in solid iron is relatively insensitive to temperature, decreasing from 9 to >6.5 wt.% over a range of 1500 K at 70 GPa. These suggest that the inner core is composed solely of the hcp phase, when the silicon content is up to 7 wt.% that likely accounts for the inner core density deficit as well as for the Mg/Si ratio and the Si isotopic composition of the mantle. Additionally, the present experiments demonstrate that the incorporation of silicon in iron expands the stability of hcp with respect to that of fcc.

    Original languageEnglish
    Pages (from-to)11-19
    Number of pages9
    JournalEarth and Planetary Science Letters
    Volume418
    DOIs
    Publication statusPublished - May 5 2015

    Keywords

    • Diamond-anvil cell
    • High pressure
    • Inner core
    • Iron-silicon alloy

    ASJC Scopus subject areas

    • Geophysics
    • Geochemistry and Petrology
    • Earth and Planetary Sciences (miscellaneous)
    • Space and Planetary Science

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